Independently organized hackathons like AngelHack need to charge to ensure long-term sustainability of the event and ensure you're getting certain amenities that you should expect from a quality hack. If you've ever been to a Facebook hackathon you can tell they spend easily 20k between setup, employees, food costs, travel, and prizes.
If PenApps isn't charging yet, then that's because they are being subsidized by UPenn, which is an awesome luxury that most potential organizers will not have.
Here's a breakdown of other costs:
--food ----< 50 people >>> (3 Meals at $6 pp) = $300 (sandwiches, pizza, bagel breakfast) >>> (3 meals at $10 pp) = $500 (with this you can get a well-priced taco buffet, pizza, snacks, bagel breakfast)
--drinks ----< 50 people >>>> $3 pp = $150 ....bubble tea would be much more pricey, but also much more awesome.
Also note that gummy bears can be purchased in 5 lbs. packs for $16 http://www.amazon.com/Haribo-Gummi-Candy-Gold-Bears-5-Pound/....